EDIBLE OILS AND FATS. 



21 



This is only approximately correct, as the correction varies for different oils, but 

 will satisfy ordinary requirements. If a higher degree of accuracy is desired, the 

 factors given in the following table may be employed, but to obtain the best results 

 the determination must be made at standard temperature. 



Factors for calculating specific gravity. a 



The following table gives correction for solid fats: b 



Factors for calculating specific gravity. 



(b) DETERMINATION AT THE TEMPERATURE OF BOILING WATER. c 



(1) Standardization of flasks. 



First method. Use a small specific gravity flask of from 25 to 30 cc capacity. The 

 flask is to be thoroughly washed with hot water, alcohol, and ether, and then dried. 

 After cooling in a desiccator the weight of the flask and stopper is accurately 

 determined. 



The flask is filled with freshly boiled and still hot distilled water and placed in a 

 bath of pure distilled water. The water of the bath is kept in brisk ebullition for 

 thirty minutes, any evaporation from the flask being replaced by the addition of 

 boiling distilled water. The stopper, previously heated to 100, is then inserted, the 

 flask removed, wiped dry, and after it has nearly cooled to room temperature placed 

 in the balance, and weighed when balance temperature is reached. 



Second method. d The following formula may be used for calculating the weight of 

 water (W T ) which a given flask will hold at T (weighed in air with brass weights 

 at the temperature of the room) from the weight of water (W l ) (weighed in air with 

 brass weights at the temperature of the room) contained therein at t: 



eF=the density of water at T. 



d'=the density of water at t. 



y=the coefficient of cubical expansion of glass. e 



Allen, Com. Org. Anal., 3d ed., vol. 2, pt. 1, p. 33. 



> Allen, Com. Org. Anal., 3d.ed., vol. 2, pt. 1, p. 32. 



U. S. Dept. of Agr., Div. of Chem., Bui. 46 revised, p. 33. 



*E. E. Ewell, U. S. Dept. Agr., Div. Chem., Bui. 62, p. 125. 



This factor is commonly given as 0.000026, but it varies considerably. Schulze (Ztschr. anal. 

 Chem., 1882, '21, 1C.7-177) found the glass used by him varied from 0.0000288 to 0.0000305; an average of 

 theM- is 0.0000296. Ewell has used 0.000028 in his work, U. S. Dept. of Agr., Div. of Chem., Bui. 62, p. 121. 



